1. Field of the Invention
The present invention pertains to a coupling or connector mechanism for remote release of an elongated coiled tubing string from a downhole tool so that the tubing string can be retrieved without an enlarged diameter element connected to the lower end of the tubing.
2. Background
The use of coilable steel tubing and similar relatively thin-walled tubing strings for handling downhole tools and other wellbore operations has become increasingly popular. Coilable tubing, in particular, is attractive in that a substantial length of tube may be stored on a spool or reel and uncoiled as required for insertion in the wellbore for inserting and operating various types of tools and for carrying out other wellbore operations. One disadvantage of using this type of tubing, particularly for the insertion and operation of downhole tools, is the predisposition of the tubing to early failure due to the stresses imposed on the tubing from repeated coiling and uncoiling operations. If a tool becomes stuck in the wellbore, it is very likely that the tubing will be parted during an attempt to pull the tubing string and tool out of the well and resulting in a difficult "fishing" or retrieval operation for the length of tubing and the tool left in the well after the tubing failure. Certain types of releasable connectors have been developed for releasing a tubing string from a downhole tool in the event of failure or the tool becoming stuck in the wellbore. However, known types of releasable connectors have an enlarged diameter portion which remains connected to the tubing string and may be the source of interference with respect to being able to withdraw the tubing string from the wellbore.
Accordingly, it has been recognized that it would be desirable to provide a releasable connector or coupling for elongated tubing strings including, in particular, coilable tubing wherein the tubing may be released from the downhole tool and the connector body without having any element connected to the bottom of the tubing which is larger or significantly larger than the diameter of the tubing itself. It is to this end that the present invention has been developed with a view to providing an improved connector or coupling for downhole tools and other devices wherein a tubing string, including coilable tubing, may be remotely disconnected from the downhole tool or device and retrieved from the wellbore at will.